The present invention relates to an image sensor and, more particularly, to a two-dimensional image reading system which includes a sensor member disposed over two dimensions.
The MOS image sensor, CCD image sensor, contact type image sensor, etc. have been developed for an image reading device in, for example, a facsimile machine. The MOS image sensor has an array of light responsive elements and an array of MOS transistors for scanning the output signals developed from the light responsive elements. The CCD image sensor transfers the charge representing the image information via the CCDs.
Both of the MOS image sensor and the CCD image sensor are formed on a monocrystal semiconductor substrate through the use of the IC technique. Thus, a large size sensor is difficult to form. Accordingly, the MOS image sensor and the CCD image sensor are generally combined with an optical lens system so as to form de-magnified image on the image sensor.
The optical lens system requires a predetermined optical path which prevents the reduction of the size of the image reading apparatus.
To solve the optical path problem, the contact type image sensor has been proposed, which includes a light responsive member having a size greater than or equal to the original document size. The image of the same size as the original document is formed on the light responsive memeber via an optical fiber. The contact type image sensor needs the light responsive member having the same size as the original documnet and, therefore, a uniform photoconductive layer of a considerably large size must be formed.
One type of the contact type image sensor now proposed is a one-dimensional image sensor employing a CdS photoconductive layer which is isolated to form light responsive elements aligned in a line. However, this type of the image sensor has a complicated construction which complicates the manufacturing process therefor. Furthermore, the reading speed is limited by the response speed of the photoconductive layer. If such a one-dimensional CdS image sensor is used to read two-dimensional image information, the reading speed is considerably slow because the one-dimensional sensor must be repeatedly used to read the two-dimensional information.
Moreover, it is difficult to integrally combine the CdS sensor section with switching elements through the use of the IC technique. This will increase the cost of the driver circuit.
Another type of the contact type image sensor now proposed is a one-dimensional sensor employing a continuous strip shaped photoconductor made of, for example, amorphous silicon. However, these one-dimensional image sensor are not suited for reading the two-dimensional information because the one-dimensional image sensor must be repeatedly used to scan the entire surface of the two-dimensional document. This slows down the reading speed.